Today, the level of the rated voltage of high voltage direct current, HVDC, applications is increased in the technical field of HVDC. With this development, improved HVDC cable terminations, which can withstand higher voltage levels, are required.
A HVDC cable is used for power supply in power distribution networks and power transmission networks. Generally, the HVDC cable comprises at least an inner or central live electrical conductor, e.g. made of copper or aluminium, an electrically insulating layer which circumferentially surrounds the electrical conductor, and a conductive shield, also called outer semicon, which circumferentially surrounds the insulating layer and the electrical conductor, the conductive shield being held on ground potential. Additional layers may be provided, e.g. a so called inner semicon, which is a conductive layer circumferentially surrounding the electrical conductor and located inside of the insulating layer, and an outer cable jacket circumferentially surrounding the conductive shield.
When the HVDC cable is electrically connected to other electric equipment, the HVDC cable is terminated. When terminating a HVDC cable, measures should be taken to ensure durable and reliable electrical performance and to protect the connection between the end of the HVDC cable and the electric equipment to which the end of cable is connected. When terminating a HVDC cable, the conductive shield and the electrically insulating layer, and possibly any further present layers, are terminated, or cut off, prior to the termination of the inner electrical conductor in order to expose the electrical conductor and connect it to the electric equipment.
WO2007/1147755-A1 discloses a cable termination for terminating a HVDC cable, the termination being provided with a device for electric field control including a field grading material layer adapted to be electrically connected to a live high voltage part and electrically connected to ground potential.
US2009/0071684-A1 describes a high voltage power cable termination.
DE 198 45 006-C1 discloses an overhead cable connector especially for medium voltage, where a funnel-shaped field control electrode surrounds the termination of the outer conductive shield, or screen, of the cable.
U.S. Pat. No. 6,124,549-A describes a cable termination where a non-linear stress-control layer surrounds the terminal portion of the cable and electrically contacts the semiconductive screen of the cable and electrically contacts the high voltage side.
DE 38 22 288-A1 discloses a high voltage cable junction including an outer shell filled with the electrically insulating gas SF6. The outer shell is made of metal. At the termination of the outer conductive screen or shield, a field controlling funnel is provided. At the joint of the two cables, an XLPE band and a winding formed by EPDM type material bands are provided around the cables.
U.S. Pat. No. 7,495,172-B2 describes an outdoor dry sealing end. The sealing end comprises a solid insulating body made of polymeric material. A metallic field controlling cylinder projects into the insulating body. The conductor of the cable is guided trough a metallic supporting tube located within the insulating body.
EP 2 026 438-A1 describes a cable connection device with a non-linear resistive field-grading layer. The field-grading layer is in direct contact with the end of the conductive shield, or semiconducting layer, of the cable.
WO2006/015735-A1 discloses an open-air cable sealing end for a high-voltage cable, comprising an outer shell and an electrically conducting connecting line, the outer shell extending axially with a space between its inner periphery and the connecting line, and the space is filled with an electrically insulating gas, e.g. sulphur hexafluoride, SF6.